Accuracy fix & Threat to gain/drop aggro

NOTE: This addon has been modified after the original author's version. Scroll down to see details on the changes.

Allows you to see the threat bars Blizzard had originally implemented in WoW, but disabled and removed with a patch down the road.

Uses:
As DPS you can use this to see your threat on the current DPS target.
As a healer you can see how much your heals are adding to your threat.
As a Tank you can keep accurate watch on your aggro and the next 4 players.
As a pet class (hunter, warlock, frost mage, etc.), you can see how your threat compares to that of your pet.

There is a second Threat Meter that only shows when you have a Focus Target.
As a tank this is useful so you can keep tabs on multiable mobs.

Added a seventh display option: "Threat to Gain or Lose". For the player who has aggro, this displays the amount of threat they would need to lose in order to drop aggro. For all other players, it displays the amount of threat they would need to gain in order to get aggro. Note that the amount CAN become negative, and that is not a bug. This happens if the non-tank is far away from the mob and very close to pulling aggro, then moves in range. This will not taunt the mob, but any amount of aggro gain thereafter (or aggro loss from the tank) will cause aggro to switch.

I fixed the percent threat values to make them more accurate. I think that's because one of the return values from UnitDetailedThreatSituation gets floored before it is returned. I fixed the percentage by ignoring that variable, and instead dividing the player's total threat by the tank's total threat. Note that in situations where a aggro is being held by a non-group-member, this cannot be fixed, and the less accurate default values are used.

1.5.6.2: modified from version 1.5.6.2. The more accurate scaledPercent is no longer used in my calculations, but I left it in there anyway, just in case it needs to be used elsewhere.